Calculating Duration between multiple dates

Hi! We have 6 date columns (for budget negotiations back and forth for instance). We want to calculate the duration of net days from columns 1-6, however, sometimes they may end at 3 or 4 negotiations so we need to calculate the duration from 1 to the last existing date entered between 1-6.
Any help on how to structure this would be great!
Answers
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Hey @Jlaustse
Try this
=NETDAYS([Column1]@row, MAX([Column2]@row, [Column3]@row, [Column4]@row, [Column5]@row, [Column6]@row))
*If the columns are contiguous, you can simply the MAX function using [Column2]@row:[Column6]@row
AFTER I verify the formula is working, because dates often cause errors, I wrap the entire formula in an IFERROR
=IFERROR(NETDAYS([Column1]@row, MAX([Column2]@row, [Column3]@row, [Column4]@row, [Column5]@row, [Column6]@row)),0)
cheers
Kelly